Field of the Invention
The present invention relates to a positive and negative rotation gas dynamic pressure bearing, a spindle motor, and a rotator device which are able to open and close a conducting hole to generate a lubricating function of a pump-out effect without an electromagnetic switching valve, and which are able to decrease run out because dynamic pressures generating at dynamic pressure generating grooves arranged equally toward a circumference direction during rotation and generating a lubricating function of a pump-in effect to close the conducting hole are all equal.
A positive and negative rotation gas dynamic pressure bearing is a gas dynamic pressure bearing which generates a lubricating function of a pump-in effect to increase dynamic pressure at central portions of the dynamic pressure generating grooves taking in lubricating gas from both ends of the dynamic pressure generating grooves during rotation in one of positive and negative rotations, and which generates a lubrication function of a pump-out effect to increase dynamic pressure at both ends of the dynamic pressure generating grooves and to receive a supply of lubricating gas from the central portions middle of the dynamic pressure generating grooves during rotation in the other of the positive and negative rotations.
As conventional positive and negative rotation gas dynamic pressure bearings, two articles are disclosed: "Positive and negative rotation herringbone journal gas bearing using both of pump-in type and pump-out type", Vol. 58, No. 555 in collection published by Mechanical Society of Japan (article No. 92-0550, Article 1, hereafter), and "Positive and negative rotation gas lubrication disc thrust dynamic pressure group bearing", Vol. 59, No. 568 in collection published by Mechanical Society of Japan (article No. 93-0465, Article 2, hereafter.)
In Article 1, a plurality of herringbone dynamic pressure generating grooves which are substantially V-shaped and shallow are formed with equal arrangement toward a circumference direction at an outer circumference surface of a shaft constituting a rotation bearing member. Three conducting holes are bored at a sleeve constituting a bearing stationary member supporting the shaft and are disposed at center portions of herringbone dynamic pressure generating grooves at intervals of 120 degrees, and the conducting holes become supplying paths of the air outside when the three conducting holes generate a lubricating function of a pump-out effect.
In Article 2, herringbone dynamic pressure generating grooves which are substantially L-shaped are formed with equal arrangement toward a circumference direction at an annular plate shape thrust bearing stationary member. Conducting holes passing through the thrust bearing stationary member are bored at center portions of herringbone dynamic pressure generating grooves at intervals of 120 degrees, and the conducting holes become supplying paths of the air outside when the conducting holes generates a lubricating function of a pump-out effect.
In both of Article 1 and Article 2, since as an electromagnetic switching valve shielding the conductive hole, a sensor detecting positive rotation and negative rotation, and a switch circuit switching open and closing operations of the electromagnetic switching valve by signal of the sensor are needed, there is a weak point that manufacturing cost is high and maintenance is needed comparing one direction rotation gas dynamic pressure bearing.
An object of the present invention is to provide a positive and negative rotation gas dynamic pressure bearing, a spindle motor, and a rotator device having a bearing construction generating a lubricating function of a pump-in effect increasing dynamic pressure at central portions of the dynamic pressure generating grooves taking in lubricating gas from both ends of the dynamic pressure generating grooves during rotation in one of positive and negative rotations, and during rotation of in the other of positive and negative rotations generating a lubricating function of a pump-out effect increasing dynamic pressure at both ends of the dynamic pressure generating grooves supplying lubricating gas to central portions of the dynamic pressure generating grooves through the conducting hole. Particularly, by rotating with the bearing movable member and by forming a self-switch valve opening and shutting the conducting hole taking in air depending on the rotation direction, the electromagnetic switching valve, the sensor, and the switch circuit are not needed. Dynamic pressures generating at dynamic pressure generating grooves equally arranged toward a circumference direction are all equal during rotation generating a lubricating function of a pump-in effect by that the self-switch valve shuts the conducting hole so as to decrease run out of rotation.